The objective of these studies is to assess the toxicologic and carcinogenic effects of 3,3'-dimethylbenzidine, 3,3'-dimethoxybenzidine, C.I. Direct Blue 15, and C.I. Acid Red 114. These chemicals, all administered in the drinking water, will be studied in male and female F 344/N rats for periods of 14 days, 13 weeks, and 2 years. The studies are part of the National Toxicology Program's "Benzidine Dye Initiative". The results of the chronic studies will be interpreted in the light of additional studies (now completed) that were conducted to characterize the genetic toxicology and chemical disposition of these prototypical as well as other structurally-related chemicals.